To ensure the safety of the passengers and crewmembers in case of a depressurization accident or the occurrence of smoke in the aircraft, aviation regulations require on board all airliners a safety oxygen supply circuit able to supply each passenger and crewmember with an oxygen flow rate which is function of the cabin altitude.
A mask and harness system is used to provide breathing oxygen. The mask system has a face seal, a pneumatically-actuated harness, and a regulator to control the flow of oxygen. The regulator comprises an inlet connected to an oxygen source and an outlet to exhaust the breathed gas outside. The outlet aperture is controlled by a movable valve so that the valve is in an open position when the crewmember breathes out and is in a closed position when the crewmember breathes in.
The system is designed for a required five-second donning with one hand.
Such breathing mask is well-known in the art as an on-demand breathing mask. The demand regulators of these breathing masks are known from the documents FR 2,781,381 or FR 2,827,179 disclosing a pneumatic demand regulator, or from WO2006/005372 disclosing an electro-pneumatic demand regulator.
However, aviation regulation often requires that at least one crewmember of an airplane wears permanently a breathing mask when the airplane cruises above a predetermined altitude so that, in case of an abrupt depressurization of the cabin, the crewmember can continue to control the airplane.
But the conventional on-demand breathing mask generates an inhalation resistance and, therefore, an increased work of breathing which results in fatigue and discomfort. This problem becomes more acute when the breathing mask must be worn permanently for many hours.
Another problem is related to the oxygen consumption generated by the permanent use of the breathing mask.
To solve, at least partially, these problems, the applicant has disclosed in the patent application having the filing number QT/EP2006/004586 a breathing mask of the above type in which an auxiliary channel is used to connect the face seal of the breathing mask to the ambient air so that there is no sufficient reduction of pressure inside the breathing mask to cause the regulator to dispense oxygen. A means is supplied to regulate flow through the auxiliary channel. The regulating means has a closed position in which flow is blocked and an open position in which flow is enabled. A biasing force is applied to the flow regulating means to maintain it in the closed position. The user may manually move the flow regulating means into the open position where a latch is deployed to maintain the flow regulating means in the open position. The latch may subsequently be released by the user when desired to revert the flow regulating means to the closed position. A pressure sensing means releases automatically the latch upon decrease in the cabin pressure, allowing the flow regulating means to revert to the closed position without action of the user upon such a decrease in cabin pressure.
However, such auxiliary channel has the inconvenience to modify substantially the breathing mask and to increase its complexity.